1. Field of the Invention
The present invention pertains to stackable riser sections and riser covers for access risers. More particularly, the present invention pertains to connecting a series of riser sections in a way that provides improved vertical support that minimizes the effect of frost heaving and other forces due to vertical ground movement, and resists rotational forces resulting from lateral ground movement and to a removable riser cover for stackable riser sections. It further relates to the configuration of a riser cover that provides a fluid and gas tight seal to a riser section, and to structure to facilitate its removal from a riser section as well as facilitating locating the cover under ground and to the stacking of a plurality of riser covers for compact and stable shipment or storage. It also relates to a system and method of maintaining the position and shape of a riser section while the riser section is being anchored in concrete by using the riser cover for positioning and support during the anchoring process.
2. Discussion
Meters, splices, junction boxes, and other components of buried utility systems are often located inside hand-holes or manholes to enable easy access by utility workers from above ground. Often, utility systems provide such access facilities at key points, such as a major bend in an underground cable/conduit run or location of water or gas meters and other equipment requiring servicing or inspection. Such access facilities have been constructed using pre-formed or poured concrete side retaining walls. Concrete can be expensive, particularly where the application requires a non-standard size or length, in which case setting forms and pouring concrete adds time and expense. Also, over time, the concrete can crack due to forces caused, for example, by freezing and thawing or by heavy vehicles being driven over the top of the manhole. Tiled sidewalls and concrete block are examples of other labor intensive alternatives.
Injection molded, plastic, stackable riser sections made of high density polyethylene and other rigid, light weight polymeric material are known in the art and provide a less expensive, standardized alternative that lends itself to rapid on-site customization. Riser sections can be manufactured in various heights and diameters, and a series of identically sized riser sections can be stacked to achieve a desired depth.
Depending on the soil characteristics and overhead traffic, the vertical, horizontal, and rotational forces placed upon these riser sections can be considerable. A major shortcoming of plastic riser sections lies in their tendency to deform or break when subjected to such forces. The use of vertical and horizontal strengthening ribs to alleviate this tendency is common. When placed along the exterior of the sidewall, however, these reinforcing ribs themselves often are subjected to the same vertical and horizontal forces they are intended to protect against.
U.S. Pat. No. 5,852,901 for a xe2x80x9cStackable Riser for On-Site Waste and Drainage Systems,xe2x80x9d issued to Meyers, illustrates one prior art design of a plastic riser section for forming a depth-adjustable, grade-level access for underground components. The Meyers riser sections form a rigid structure intended to support heavy loads applied to the grade level access lid. Identical riser sections reinforced along portions of both the inner and outer walls are stacked one on top of the other utilizing a single tongue and groove connection. A horizontal rib extending outward along the circumference of the external surface of the side wall of each cylindrical riser section and a plurality of vertical ribs, also on the external surface of the riser, individually anchor each riser section in the ground. A plurality of riser sections can be stacked to form a vertical, air-tight, liquid-tight, and gas-tight riser stack and cover system.
The shifting of the ground surrounding the riser stack disclosed in the Meyers patent can twist and move the stacked riser sections, knocking them out of alignment. Eventually, the shifting can lead to rupture of the stacked riser sections"" sidewall. The presence of external horizontal and vertical reinforcing ribs extending along the wall of each riser, while strengthening the riser section sidewalls, also exacerbates this problem because shifting soil applies force against each exposed rib. The configuration of the tongue and groove arrangement of the riser sections disclosed in the Meyers patent also precludes the placement of supporting ribs along the full vertical length of the interior riser section wall, which lessens the sidewall""s resistance to forces exerted by the shifting of the soil abutting the sidewalls and external ribs.
It is also common for one section of a riser stack to be anchored in concrete. The anchored section, generally the section defining the opening into the chamber defined by the concrete walls of an underground component, is then used as a base for the riser. Other sections are stacked on top of the anchored section to the desired height of the riser. This process involves positioning and securing a hollow riser section inside a concrete mold or form of a shape for forming the top wall of a chamber or underground component. The concrete is then poured into the mold around the riser section. The riser section can be subjected to stress during this process and may deform or break under these conditions. In addition, because it can be made of light weight plastic, it can be difficult to keep the riser section in place while pouring the concrete because the riser section may tend to float in the concrete.
One method of preventing deformities in the riser section during anchoring involves the addition of cross braces to the inside of the riser. The braces can conform to the shape of the riser section or can simply be metal or wood rods sufficiently long to provide lateral support for opposed riser section sidewalls. This solution is imperfect, however, because the sidewall support thus provided is not uniform and may still permit deformities to occur. Additionally, this solution adds to the cost and time needed to anchor a riser section in concrete.
A variety of methods have been employed to keep a riser section in place during the anchoring process, with almost all involving construction on an ad-hoc basis in the field. One method is to place one or more elastic straps or rubber cords across the top of the concrete form, ensuring contact with the riser section in order to hold it down. This does not address side-to-side movement. One way to attempt to control this is by placing a weight or heavy object, such as a concrete block, on top of the riser section and under the elastic strap. The weight, however, may create an additional problem because it adds to the stresses being applied to the riser section sidewalls during placement of the concrete.
Another difficulty with the use of plastic riser sections is locating the riser stack after installation. Many riser access facilities are located in areas where it is easy to locate the opening, such as in streets, sidewalks, and other paved areas, or where the opening is above grade. However, access facilities frequently are located below grade level and are covered by soil and grass or other vegetation. In these situations, it may be difficult to locate the opening of the access facility when required. While a metal cover may be located using a metal detector, plastic stackable riser sections may not. One method of making plastic riser stacks locatable is to mold one or more metal rods into the concrete wall into which a plastic riser section has been anchored. Because the concrete wall is typically lower in the ground than the riser cover, a significant amount of metal is required in order to ensure it can be detected at the surface using a conventional metal detector. This method may also create an added step in casting the wall of the box into which the bottom riser section is anchored.
The riser sections and cover of the present invention overcome the foregoing shortcomings. In the preferred embodiment, the stackable riser sections of the present invention have a hollow, cylindrical configuration, although configurations other than cylindrical may be used. The sidewall of the riser section includes a channel end and a tapered end. In the preferred embodiment, the riser section has a nearly smooth exterior surface from which projects outwardly a detachable anchor tab that may run along substantially the full circumference of the riser. The channel end of the riser section sidewall includes two adjoining channels which are defined by interior, middle, and exterior walls that extend down from a horizontal ledge on the interior surface of the side wall at the channel end. The walls project concentrically with, or (in the case of riser sections having, for example, a square or rectangular cross-section) parallel to, the sidewall. The opposite, or tapered, end of the riser section sidewall terminates in a portion tapered to a narrower thickness at the end. A plurality of vertical reinforcing ribs are spaced around the interior surface of the cylindrical sidewall of the riser. Because in the preferred embodiment the ribs extend from the horizontal ledge at or near the channel end to the distal end of the tapered end of the riser section sidewall, they strengthen the sidewall in the area of the joint between each pair of stacked riser sections.
In the preferred embodiment, the interior surface of the sidewall also includes at least one, and preferably more than one, boss extending vertically from the horizontal ledge near the channel end to the distal end of the tapered end of the riser. Each boss is adapted to receive a screw, or other fastener, that extends through he horizontal ledge of a riser section stacked above the tapered end for securing that riser section stacked on top of the first riser section. The bosses also may receive a screw to attach a cover at the top of a riser stack.
The tapered end of the riser section sidewall is configured to mate with the two concentric channels of either another riser section or a cover. The radially outer channel is shallower than the inner channel in the preferred embodiment and accepts the tapered end of the sidewall of another riser section on which it is placed. An O-ring placed in the outer channel can be used to effect a water-tight and gas-tight seal between two stacked riser sections (or between a riser section and a cover).
The radially inner channel is wider than the outer channel, and accepts the interior vertical support ribs and bosses of a riser section on which it rests. The middle wall of the channel end includes slots that permit positioning of the bosses and ribs within the inner channel of a riser section positioned above the ribs and bosses. Projections on the bottom of the horizontal ledge and aligned with the slots support the upper riser section on the bosses as ribs of the lower riser section.
In the preferred embodiment, a detachable anchor tab on the exterior surface of the riser section sidewall serves to anchor the lower-most riser section in concrete, for example, in the wall of a concrete distribution box. The concrete is poured around the riser section and its anchor tab, thereby anchoring the bottom riser section after the concrete hardens. Another identical riser section may be placed on top of the bottom riser section, with the tapered end of the bottom riser section mating with the channel end of the riser section placed on top of the bottom riser section. The anchor tab on each of the riser sections stacked above the bottom riser section (i.e., above the riser section anchored in the concrete box) in a given stack can be detached by tearing it away from the exterior of the sidewall. In the preferred embodiment, the anchor tab includes a handle for this purpose. Tearing away the anchor tabs on the riser sections that are not anchored in concrete gives the riser stack a nearly smooth exterior surface, thereby minimizing the forces exerted on the riser stack by movement of the soil in contact with the riser stack.
There also is provided, in the preferred embodiment, a cover adapted to be secured to the top of a riser section. Like the stackable riser, the preferred shape is cylindrical, but other configurations, such as square, rectangular or elliptical may be used.
The cover has a top surface and a bottom surface, with the top surface being nearly smooth and slightly convex in the preferred embodiment. A sidewall of the cover depends from the top surface. It includes a channel end similar to the channel end of the riser sections. The channel end includes two adjacent concentric channels defined by inner middle and outer walls. The outer wall defines the sidewall outer surface of the cover.
Handles to aid in removal of the cover are provided on the top surface of the cover. In the preferred embodiment, each handle pivots about a support shaft which is attached to the cover by a screw or other fastener. The support shaft is set inside a recess adjacent the top surface, and the handle pivots between a position generally perpendicular to the top surface and a position inside the recess, substantially parallel to and flush with the top surface. The recess is large enough to accept the entire handle.
The cover preferably has at least two wells open to the top surface. They may be substantially 180xc2x0 apart in the preferred embodiment, although another embodiment may have only one well or more than two wells. The wells are defined by hollow posts depending from the bottom surface of the cover.
In a preferred embodiment, the hollow posts on the bottom surface extend below the bottom edge of the channel end of the cover. The posts define the wells open at the top surface, as described above. Preferably, the posts are located approximately midway between the center of the bottom surface and the cover channel, about 180xc2x0 apart from each other. In different embodiments, there may be only one post or more than two posts, in which case the posts may be located as desired on the bottom surface.
The posts extending from the bottom surface of the riser cover preferably are tapered such that each is of a larger diameter where it joins the bottom surface of the cover than at its free end. There may also be a stepped change in diameter at some point between the bottom surface and the end of the post, creating a shoulder. The diameter of the free end of each post is smaller than the diameter of the hollow well formed by the post. The tapered design of each post and well allows stacking of multiple riser covers by placing the posts of one riser cover into corresponding wells in the top of another riser cover. Stacking of riser covers is beneficial for storage and for shipping multiple riser covers.
The wells open to the top of the riser cover may receive a metal bar prior to completion of the underground component such as a concrete distribution box installation in the field. As described above, it is common for riser covers to be buried by soil and vegetation growth. The placement of the metal bar into the well allows the cover and plastic riser sections to be located using a metal detector.
The riser cover can be used in a method to secure a riser section while the riser section is being molded in concrete (i.e., while the wet, viscous concrete is poured and is setting). In the preferred method of securing a riser section in concrete, a mounting bracket is provided which is adapted to receive the posts depending from the bottom surface of a cover. The mounting bracket adapted to be secured to the wall of a concrete form preferably has two (or other number corresponding to the number of posts in the cover) holes configured to accept and releasably retain the posts of the riser cover. The holes are sized and tapered such that when the posts are pushed into the holes, the sides of the holes grip the posts in a fraction fit and thereby firmly secure the cover to the bracket.
During the concrete casting operation, the mounting bracket is secured to a horizontal wall of a concrete form at a desired location where the access riser is to be provided. The riser section is positioned on the form surrounding the bracket. A riser cover, positioned with the channel end of the cover engaged with the tapered end of the riser section is attached to the bracket. The posts of the cover are aligned with, and pushed into, the holes on the mounting bracket such that the posts are gripped securely by the bracket. The riser section is thus positioned and secured properly relative to the bracket and, particularly, the concrete form. The riser section is also supported against deformation during a pour. Concrete sufficient to secure the riser section is then poured into the form and allowed to cure. The riser cover, which has not been in contact with the concrete, is then removed from the riser section by pulling the posts out of the holes in the mounting bracket. The mounting bracket may then be removed and the form disassembled from the poured concrete wall.
It is an object of the present invention to provide an improved connection configuration that resists rotational forces exerted on one or more riser sections in an interconnected system.
It is another object of the present invention to provide improved reinforcement of the sidewalls of riser sections stacked one on top of the other.
It is still another object of the present invention to provide a detachable anchor on the exterior surface of a riser section, the anchor being used when the riser section is to be molded in concrete, and removed when the riser section is to be in contact with soil.
It is a further object of the present invention to provide a riser section adapted for being anchored in concrete, while at the same time minimizing the susceptibility of a riser stack to forces caused by the ground next to the stack shifting.
It is a further object of the present invention to provide a riser cover having recessed handles such that the riser cover will have an essentially smooth top exterior surface when the handles are not in use.
It is still a further object of the present invention to provide a method for positioning and supporting a riser section being molded in concrete to minimize the susceptibility of movement of the riser section during the molding process and resist deformation of the riser section due to the forces exerted by the concrete while being poured.
It is still a further object of the present invention to provide a riser cover adapted for being stacked one on top of another with the posts of the top cover projecting into the wells of the bottom cover such that multiple covers may be stacked compactly and stably for shipping or storage.
It is another object of the present invention to provide a plastic riser cover adapted to easily receive a metal bar in order to permit the cover to be located after it has been buried in soil or other material.